Non-Uniform Aging of Commercial NMC/Graphite Lithium-Ion Batteries

Non-uniform aging of commercial
NMC/Graphite lithium-ion batteries

Abdulrahim Ayoub¹, Abdilbari Mussa²,
Maria Varini²

¹
Department of Chemical Engineering, The City College of New York, CUNY, New
York, NY 10031, USA

²
School of Chemical Engineering, Division of Applied Electrochemistry, Royal
Institute of Technology, Stockholm, Sweden

Lithium ion batteries are well-established energy storage systems
with high power and energy density. In the past few years, rechargeable lithium
ion batteries have played a major role in automotive applications; however, many
obstacles remain in long-term performance and durability. Decrease in capacity
and/or a rise in impedance leads to electrode aging, thus, dramatically degrading
the batteryÕs performance.

Herein, aging of commercial NMC/Graphite battery is investigated in
(i) calendar aged cells, stored at 22^oC
for approximately a year, (ii) cycled cells, cycled at +4C/-1C between 10-90%
SOC. Further, electrochemical analysis was done on different positions within the
electrode layer to study aging as a function of position, namely edge and
center. In this study, electrochemical impedance and capacity measurements were
the methods of choice used to characterize aging.

Calendar and cycled aged cells displayed differences in capacity
fade and impedance rise. Specifically, the cycle-aged cells showed more
pronounced losses, likely associated with the growth/formation of the
solid-electrolyte interface(SEI) and the loss of cyclable lithium. Considering
the edge and center of the same electrode layer, variations in capacity and
impedance were also noticed, possibly caused by an un-even current distribution
along the electrode.